A series of novel cotton cellulose-graft-polycaprolactone copolymers with different grafting contents were successfully prepared via ring-opening polymerization (ROP) in an ionic liquid 1-N-butyl-3-methylimidazolium chloride ([Bmim]Cl). The structures of the grafting copolymers were systematically characterized by FTIR, CP/MAS¹³C-NMR, XRD, SEM and AFM, while thermal properties were investigated by DSC and TGA. Subsequently, Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R) adsorption isotherms were representative to simulate adsorption isotherms of Cu(II) and Ni(II) ions in aqueous solution. From the comparison of different adsorption isotherm models, it was found that adsorption of Cu(II) by modified cellulose followed Langmuir, Freundlich and Temkin models, while that of Ni(II) followed the Freundlich model. The results of adsorption indicated that the selectivity sequence of metal ions on graft copolymers was Cu(II) > Ni(II) and the maximum removal capacities of Cu(II) and Ni(II) ions were 98.7% and 35.6%, respectively. Hence, the graft copolymers exhibited significant potential to be an environmentally feasible biosorbent for removal of Cu(II) and Ni(II) ions from aqueous solution.